The invention relates to a shaft seal system for a piston pump. More specifically, the invention relates to a sealing system which prevents debris from seal wear from contaminating the fluid being pumped.
Piston pumps are frequently used in high pressure applications, such as liquid chromatography. Typically, such pumps employ a shaft seal which surrounds the shaft at bottom dead center. Sealing is effected by pressing a lip portion of the seal against the shaft using a spring disposed in an annular groove in the seal. Typically, such seals are formed from polytetrafluorethylene (PTFE) impregnated with graphite fibers.
Unfortunately, such seals are subject to wear as a result of abrasion between the seal lip and the shaft. This wear causes small particles of the seal--that is, particles of PTFE or graphite fibers--to be flushed into the fluid being pumped. Such contamination of the fluid can cause damage to valves, plug capillaries and, in the case of liquid chromatography, destruction of the chromatographic separation column. Traditionally, such problems have been avoided by placing filters in the fluid downstream of the pump to capture the seal debris. However, this approach suffers from the drawbacks of increased maintenance due to the need for frequent filter replacement and increased complexity of the fluid system.
Accordingly, it would be desirable to provide a seal which prevented seal wear debris from contaminating the fluid being pumped.